Australia has one of the lowest population densities in the world. With a total population of 23 million and a land area of over 7.6 million km² its density is around 3 people per km².
This is very low compared to the Monoco, the most densely populated area in the world with 26150 people per km².
But this is NOT why it is underpopulated. Low population density does always = underpopulation.
Underpopulated countries have too few people to make full use of the resources they have.
Australia is rich in natural resources with large reserves of natural gas, oil, gold, uranium and metal ores.
Uranium is important in the development of nuclear power around the world. Australia attracts migrant workers to support the exploitation of these natural resources.
Australia has the 9th highest immigrant population in the world with 6.7 million, which makes up 28.2% of its population.